The broad objective of this project is to contribute toward a better understanding of the molecular processes that underlie muscle contraction. Myofibrillar proteins are studied by chemical, physico- chemical and enzymatic methods. Their interactions with each other and with nucleotides and metal ions give us models of the processes occurring in muscle. The gaps between events on the molecular level and the more highly organized systems are bridged by electron microscopic investigations of protein molecules, their aggregates and various subcellular structures isolated from muscle. Comparative investigations are carried out to establish correlations between function and chemical constituents in fast and slow skeletal and in cardiac muscle, and attempts are made to extend the work to disorders of these muscles.